Novel Nanocrystallization Technique for Low Temperature Plasma Nitriding of Stainless Steel

A novel nanocrystallization technique of surface mechanical attrition treatment (SMAT) has been introduced for low temperature plasma nitriding of stainless steel. This research work was performed by a research group led by Prof. XUE Qunji from the CAS Lanzhou Institute of Chemical Physics in cooperation with Prof. Jian Lu of University of Technology of Troyes. The newest results of this research shows that the longstanding difficulty of the stainless steels nitriding may be solved by surface nano-structrued pre-treatment and the related research work was reported by Acta Materialia (Vol. 54, issue 20, 2006).

The researchers find that a plastic deformation surface layer with nanocrystalline grains can be produced on the surface of the important engineering material, AISI 321 austenitic stainless steel, by means of SMAT. The nano-structured sample and the coarse grain sample were then nitrided simultaneously using pulsed-DC glow discharge plasma technique at low temperature. The results show that the plasma nitriding of AISI 321 steel can be enhanced considerably by means of SMAT process before nitriding, and a much thicker nitrogen diffusion layer with higher hardness was obtained for the SMAT samples when compared with un-SMAT samples. In addition, the wear resistance and load capacity of the nitrided layers on the SMAT samples was much higher than that of the un-SMAT samples due to the thicker S phase case and the gradient nitrogen diffusion layer.

This research conducts nanocrystallization technique and combines the conventional nitriding treatment on strengthening of stainless steel and, as a result, the high brittleness and poor case depth of the nitrided layer can be eliminated. Our results exhibit an application potential of nanotechnology for commercial engineering materials.

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